On the impact of meson mixing on Bs→ ϕee angular observables at low q2

Abstract

Decays based on the b → sγ transition are expected to yield left-handed photons in the Standard Model, but could be particularly sensitive to New Physics contributions modifying the short-distance Wilson coefficients mathcal{C} 7 and mathcal{C} 7′ defined in the low-energy Effective Field Theory. These coefficients can be determined by combining observables of several modes, among which Bs → ϕee at low q2, in a kinematic range where the photon-pole is dominant. We investigate the impact of Bs − overline{B} s mixing on the angular observables available for this mode, which induces a time-dependent modulation governed by interference terms between mixing and decay that are sensitive to the moduli and phases of mathcal{C} 7 and mathcal{C} 7′. These interference terms can be extracted through a time-dependent analysis but they also affect time-integrated observables. In particular, we show that the asymmetries {A}_T^{(2)} and {A}_T^{left(operatorname{Im}right); CP} receive terms of potentially similar size from mixing-independent and mixing-induced terms, and we discuss how the constraints coming from the angular analysis of Bs→ ϕee at low q2 should be interpreted in the presence of mixing.